This invention relates to apparatus for reading, writing or erasing information from and to optical disks. In particular, the invention relates to read-only disks (e.g., CD-ROMs), write-once-read-many (WORM) disks, and erasable magneto-optic disks, for example.
The optical subsystem design required to write, read and erase information in an optical recording system has evolved over time to follow the developments in recording media technology and changes in applications. Early designs were configured around gas lasers rather than semiconductor (diode) lasers mainly due to the lack of adequate power and reliability of early diode lasers. Driven by the mass consumer market for CD players, the situation has changed. Cheap, high power diode lasers are now available in large quantities. With the availability of these diode lasers and the development of write-once and erasable media for an emerging mass market for optical storage, the thrust for optical recording research and development has now shifted toward the design of more compact drives giving a higher level of performance at a lower price to satisfy the needs for a true mass market. A prime concern in this development process is the miniaturization of the optical subsystem, or head, required for all optical storage applications. This trend is expected to continue as the range of applications for optical storage broadens and attempts are made to compete directly with alternative magnetic recording technologies.
The current, state-of-the-art optical head technology uses free-space optics based on assembling precisely aligned bulk optic components. The two major problems with this conventional approach are the cost and weight of the bulk optical assembly. The large mass of a typical conventional magneto-optic head (about 100 g) results in relatively long access times (e.g., 90 msec for magneto-optic heads vs. 15 msec for non-optical, hard disk magnetic heads). In the most advanced recent designs of optical heads only a part of the optical subsystem moves. This design has reduced the moving mass of the head to 6 g and the access time to 20 msec. However, decreased access time was achieved at the cost of a significant increase in complexity of the mechanics and optics of the disk drive, with concomitant higher cost.
Thus, a need remains in the art for a low mass, fast access time optical head which can be fabricated at relatively low cost.